Enhanced tolerance to flue gas contaminants on carbon dioxide capture using amine-functionalized multiwalled carbon nanotubes

The adsorption behavior of adsorbents for carbon dioxide can be significantly affected by flue gas contaminants. In this work, we examined the performance of tetraethylenepentamine (TEPA) impregnated industrial grade multiwalled carbon nanotubes (IG-MWCNTs) in trace amounts of flue gas contaminants such as H₂O, NO, and SO₂. It was observed that H₂O and NO had a minimal impact on CO₂ adsorption capacity, while the effect of SO₂ on CO₂ adsorption was influenced by adsorption temperature and SO₂ concentration. Compared with silica-based adsorbents, i.e., TEPA-impregnated MCM-41, amine-functionalized IG-MWCNTs show significantly better tolerance to H₂O and SO₂. In addition, we examined the variation of CO₂ adsorption with and without SO₂ with various experimental methods (N₂ adsorption/desorption isotherms, X-ray diffraction, and differential scanning calorimetry analysis) and molecular simulation. Experimental results show that irreversible sulfate/sulphite species deposited into the adsorbent contributes to the decrease on CO₂ adsorption, while the results from simulation studies reveal that the enthalpy difference between the isolated TEPA with SO₂ and TEPA⋯SO₂ (ΔH(TEPA⋯SO₂)) is larger than that of CO₂ (ΔH(TEPA⋯CO₂)), indicating that SO₂ has a stronger reaction activity with TEPA than CO₂. The increase of the ratio of ΔH(TEPA⋯SO₂)/ΔH(TEPA⋯CO₂) with increasing temperature illustrates that the difference of CO₂ adsorption capacity with and without SO₂ increases with elevated temperatures.